1. Field of the Invention
The present invention relates to an exhaust system for an engine that includes an exhaust manifold having a structure such that an end portion of a collecting section where pipes connected to respective cylinders of an engine are collected is inserted and fixed in an upstream side end portion of a joint tube member by which the exhaust manifold and an exhaust pipe are connected with each other.
2. Description of the Related Art
A conventional exhaust system for an engine is disclosed in Japanese Patent Application Laid-open No. 2001-055920. As shown in FIG. 8, this conventional exhaust system has an exhaust manifold that has a structure such that a pipe end of a collecting section 105 where pipes 101 to 104 connected to respective cylinders, not shown, of an engine are collected is inserted and fixed in an upstream side end portion of a joint tube member 106 having a cylindrical shape to receive the pipe end of a collecting section 105 and an exhaust pipe, not shown.
Further, FIG. 9A shows an enlarged perspective view describing a connection state of the joint tube member 106 and the collecting section 105 before assembling, and FIG. 9B shows a perspective view describing a connection state of the conventional joint tube member 106 and the collecting section 105 after assembling. As shown in FIG. 9A and FIG. 9B, the joint tube member 106 is formed in a state that a partition plate 109 is sandwiched between an upper joint part 107 and a lower joint part 108 to form two exhaust passages therein so as to prevent exhaust gas interference outputted from the pipes 101 to 104.
Furthermore, FIG. 10 shows a cross-sectional view taken along the line S10-S10 in FIG. 8. As shown in FIG. 10, between an upstream side end portion of the partition plate 109 and an end portion of the collecting section 105, a clearance W with a predetermined distance is generally provided for allowing a relative displacement of the collecting section 105 and the joint tube member 106 due to their thermal expansion.
However, in the conventional exhaust system, the position of the partition plate 109 is occasionally displaced from an intended position when the upper joint part 107, the lower joint part 108, and the partition plate 109 are fixed by welding in a state that the partition plate 109 is sandwiched between the upper joint part 107 and the lower joint part 108, and thus the partition plate 109 cannot be fixed precisely with respect to the joint tube member 106. Consequently, there has been a problem that the clearance W varies in products.
Incidentally, the clearance W cannot be adjusted or inspected from outside after both of them are assembled, because the end portion of the collecting section 105 is inserted and fixed in the upstream side end portion of the joint tube member 106.
Further, when upstream side end portions of both joining parts 107 and 108 of the upper joint part 107 and the lower joint part 108 are joined in the radial direction, a gap WA is generated as shown in FIG. 9B when the end portion of the collecting section 105 is inserted and fixed in the upstream side end portion. Accordingly, a large welding tip should be used to fill this gap WA, so that a welding work thereof requires much labor and time, and moreover welding sputter may enter inside the joint tube member 106.
The present invention has been made to solve the above-described problems, and an object thereof is to provide an exhaust system that includes an exhaust manifold in which a clearance can be formed appropriately between a partition plate and an end portion of a collecting section by positioning and fixing the partition plate precisely with respect to a joint tube member.